On the eve of potentially decisive Super Tuesday voting, the White House said anxious Republican leaders in Washington have only themselves to blame for Donald Trump’s near solid grip on the party’s presidential nomination.

He said Republican House and Senate leaders have created a power vacuum through their failure to work with President Obama.

Mr. Trump, who is poised to win 10 out of the 12 states holding contests Tuesday, is Mr. Obama’s worst nightmare as a possible successor. The businessman has angered the president with everything from his campaign slogan of “Make America Great Again” to his vow to build a wall along the Mexican border and his proposal to bar Muslims temporarily from entering the U.S.

Mr. Earnest said Monday that the president still believes Mr. Trump won’t become the next president and that the American voters will show more wisdom as the campaign proceeds. But with Mr. Trump racking up more wins and looking increasingly unstoppable to secure the Republican nomination, the White House is searching for a plausible explanation for his success.

So the president’s spokesman turned the blame on congressional Republicans. Referring to reports that establishment Republicans in Washington are expressing consternation about Mr. Trump’s “hijacking” of the party, Mr. Earnest said the fault lies with those same Republican lawmakers who are “blocking important work that needs to get done.”

“It’s not surprising to me that a Republican majority in Congress refusing to do their jobs is on the brink of being taken over by someone they say doesn’t represent their views,” Mr. Earnest said. “They have that majority, and they’re in a position where they’re not just saying ‘no’; they’re not saying anything. They’re refusing to speak.”

He cited Republicans’ rejection of Mr. Obama’s plan to close the Guantanamo Bay military prison and to transfer some of the terrorism detainees to prisons in the mainland U.S.

Democrats and Republicans alike have repeatedly blocked the proposal.

It’s an argument that might amuse Republican primary voters.

Former House Speaker John A. Boehner of Ohio lost the support of conservatives in the House and in the Republican Party base primarily because he occasionally compromised with the White House — not because he acted as a roadblock to the president’s agenda.

Mr. Earnest also referred to Senate Republicans blocking many of the president’s nominees such as Adam Szubin, a Treasury Department official who works on efforts to block financing of terrorist networks.

Senate Republicans have vowed not to grant a hearing for Mr. Obama’s pending nominee to fill a vacancy on the Supreme Court after the death of Justice Antonin Scalia. The president will discuss the nomination Tuesday at the White House with Senate Majority Leader Mitch McConnell, Kentucky Republican; Senate Minority Leader Harry Reid, Nevada Democrat; and Sens. Chuck Grassley, Iowa Republican, and Patrick J. Leahy of Vermont, respectively the chairman and ranking member on the Judiciary Committee.

The White House said Monday that Mr. Obama has tapped Brian Deese, an economic analyst who led the administration’s climate change efforts last year, to head a team to pick a Supreme Court nominee and win confirmation. White House counsel Neil Eggleston will guide the legal process, including the vetting of potential candidates.

“The president has relied on Brian in a variety of critical situations to do important work and to take on important projects,” Mr. Earnest said. “Given Brian’s performance in his other priorities, I don’t think it’s particularly surprising he would be tapped for this responsibility too.”